The invention is directed to preparing moisture vapor permeable ethylene copolymer films and articles.
Breathable films that are permeable to water vapor and impermeable to liquid are useful in a variety applications and are particularly well suited for use in disposable personal care and health care articles such as disposable diapers, adult incontinence products, feminine care absorbent products, training pants, garments and as coverings for a variety of articles. These films often provide the function of a breathable liquid impermeable barrier layer.
Breathable films exist in various forms. In one form, a breathable film includes micropores that form tortuous pathways through the film such that liquid placed in contact with one side of the film does not have a direct passage through the film to the opposite side of the film. The network of microporous channels in the film prevents liquids from passing through the film, but allows gases and water vapor to pass through the film.
In another form, a breathable film includes micropores that result from incorporating a filler, e.g., calcium carbonate, in the polymer melt, forming the polymer melt into a film, and then stretching the film. Stretching the film causes the polymer to break away from the particulate filler, which creates microporous passageways in the film. The additional processing steps required to make microporous films can increase the complexity and cost of the making the breathable film.
Breathable films can also result from the molecular structure of the polymer(s) of the film. Breathable polymers tend to have polar groups, e.g., hydrophilic groups. The polar groups of the polymer facilitate transfer of gas molecules or moisture vapor through the polymer film prepared from the breathable polymer. Breathable films have been prepared from various polymers including poly(vinyl alcohol), polyvinyl acetate, ethylene vinyl alcohol, polyurethane, ethylene methyl acrylate, ethylene methyl acrylic acid, block copolyester-copolyether, block copolyamide copolyether, and thermoplastic polyurethane.
Polymers that do not have hydrophilic groups or polar groups are considered to be non-breathable. In addition, polymers with relatively high amounts of hydrophobic groups and very small amounts of polar groups are also considered to be non-breathable. Copolymers such as ethylene vinyl acetate, ethylene n-butylacrylate carbon monoxide, and ethylene vinyl acetate carbon monoxide traditionally have been viewed as non-breathable.
Known breathable polymers tend to be more expensive than non-breathable polymers.